So while preparing modak sweet, Dolly stepped aside from kitchen & Kaamna mixed poison in that flour that was still cooking on stove.
Assuming that kadai got burnt out, Dolly/Indu noticing it discarded that poisoned flour & prepared fresh sweet again? or driver/Vivek bought modaks from a shop. Hence nothing will happen to Ritesh's mom after eating modak nor will Indu get blamed.